This invention relates to a controllable shock absorber for motor vehicles. The shock absorber is of the type that includes a damping cylinder which contains damping fluid and in which a damping piston slides. The damping piston is provided with pressure-dependent valves and is connected with a piston rod. The damping piston divides the damping cylinder into two work chambers. One of the work chambers is in hydraulic communication through a bottom valve with an equalizing chamber defined between an external tube surrounding the damping cylinder and the damping cylinder itself. There is further provided a bypass channel which interconnects the work chambers and whose flow passage section is controlled by means of two setting elements which are adjustable relative to one another as a function of the relative rotation between the piston rod and the damping cylinder during steering displacement (turning) of the wheels.
In a wheel-controlled shock absorber described in German Patent No. 4,135,607 a flow passage adjustment of the bypass channel interconnecting the working chambers of the damping cylinder is effected as a function of the displacement of the wheel relative to the vehicle chassis. The damping force exerted by the shock absorber is controlled as a function of the rotary displacement between the piston rod and the damping cylinder during steering motion of the wheels.
The bypass channel extends from the upper work chamber, situated above the damping piston, through a lateral transverse port provided in the piston rod into an axial bore thereof and further extends in a hollow control rod to a valve plunger which constitutes a first setting element and which cooperates with an aperture of a second setting element, leading to the lower work chamber. The control rod is received axially slidably in the piston rod but cannot rotate relative thereto.
Since a relatively non-rotary coupling exists between the second setting element and the damping cylinder as well as between the first setting element (valve plunger) and the piston rod, upon a steering motion of the wheel connected with the damping cylinder, relative to the chassis to which the piston rod is affixed, there will occur a relative rotary motion between the damping cylinder and the piston rod and thus between the second setting element and the valve plunger received by the second setting element. As a result, the valve plunger closes the bypass channel between the work chambers of the shock absorber.
Since in a dual-tube shock absorber the damping force in the pressing phase is essentially generated by the bottom valve situated between one of the working chambers and the equalizing chamber, the effect of the conventional bypass control is always dependent upon the magnitude of the damping force generated by the bottom valve.